I started my small business in 2020 and got COVID in Dec impacting my ability work for 23 days. Can I get the $511/day tax credit if I didn't file Schedule SE in 2019?

You might be able to get the credit. The amount will be determined when you compete your return.  

You'll have to complete Form 7202 in TurboTax once it becomes available.

Form 7202, Credits for Sick Leave and Family Leave for Certain Self-Employed Individuals is tentatively scheduled to be available in TurboTax on February 11th. 

It will not be supported in e-file, so it must be printed and you'll need to mail your return.

If you were self-employed, you can use Form 7202 to figure an amount to claim for qualified sick and family leave equivalent credits on your 2020 tax return.